University of Washington Publications in Geology The Geology of the San Juan Islands

CHANNELS

HARO STRAIT

Haro Strait is located on the west side of the San Juan Island group and forms the International boundary line in this region. It has a minimum width of about six miles and the bed of its channel, which is located near the eastern margin, has an average depth of about 900 feet. The deepest point on the map-area occurs in Haro Strait less than a mile to the north of Turn Point, on Stuart Island, where there is a depth of 1356 feet. Due to the great width and depth of Haro Strait, and also to its proximity to the Strait of Juan de Fuca, it supplies the bulk of the water that flows in and out of the Gulf of Georgia at every tide.

To the north of Stuart Island Haro Strait merges with a number of smaller channels which separate the various Canadian and American islands. Here the channel bends sharply to the eastward and its northern limit, or the point where it merges with Boundary Pass, is located near the entrance to Plumper Sound.

BOUNDARY PASS

Boundary Pass is located between Patos Islands on the east and the Canadian island, Saturna, on the west. To the northward and eastward it merges with the waters of the Gulf of Georgia, while to the southward it merges with Haro Strait. Its channel has an average depth of 600 feet, and the deepest point, which is located to the northwest of Alden Point on Patos Island, is 960 feet deep.

PRESIDENT CHANNEL

President Channel is located between Waldron Island and Orcas Island. To the northward it merges with the waters of the Gulf of Georgia, while to the southward it is continuous with San Juan Channel and with the various off-shoot channels from Haro Strait. The bed of the channel has an average depth of 600 feet and its width is about two miles.

SPRING PASSAGE

Spring Passage separates Jones Island from Orcas Island. It is about half a mile wide and the average depth of its channel is about 80 feet.

NEW CHANNEL

New Channel is located between Spieden Island and Cactus Islands. It is about one-third of a mile wide and the depth of its bed varies between 100 and 300 feet. It forms one of the connections between San Juan Channel and Haro Strait.

SPIEDEN CHANNEL

Spieden Channel is located between Spieden Island and the north end of San Juan Island. It is about a mile wide at its eastern or narrow end, and the average depth of its bed is about 350 feet, though in places it is more than 500 feet deep. Spieden Channel forms one of the connections between Haro Strait and San Juan Channel.

SAN JUAN CHANNEL

San Juan Channel separates San Juan Island from Lopez, Shaw, and Orcas islands. At its southern extremity it is known as Cattle Point Narrows. In the vicinity of Turn Island it bends abruptly to the northwestward and it finally merges with Haro Strait and President Channel. Its width and depth vary greatly. At Cattle Point Narrows it is less than a mile wide, while in other places it is more than two miles wide. The average depth is about 350 feet, but near its northern end it is more than 600 feet deep.

UPRIGHT CHANNEL

Upright Channel branches off to the northeastward from San Juan Channel and separates Lopez Island from Shaw Island. It has an average width of about a mile and the average depth of its bed is about 150 feet. To the northeastward it merges with Harney Channel.

HARNEY CHANNEL

Harney Channel separates Shaw Island from Orcas Island. At its western extremity it branches off to form Pole Pass and Wasp Passage. To the eastward it merges with Upright Channel and their combined channels finally merge with East Sound and Lopez Sound. Harney Channel has an average width of about half a mile, and the depth of its bed varies between 80 feet and 190 feet.

OBSTRUCTION PASS

Obstruction Pass is located between Orcas Island and Obstruction Island. Its average width is about 500 yards and the minimum depth of its bed is about 40 feet.

PEAVINE PASS

Peavine Pass is located between Obstruction Island and Blakeley Island. its minimum width is about 250 yards and the minimum depth of its bed is about 35 feet at low tide.

THATCHER PASS

Thatcher Pass separates Blakeley Island from Decatur Island. It has a minimum width of about half a mile and the average depth of its bed is about 180 feet. It connects Lopez Sound with Rosario Strait.

LOPEZ PASS

Lopez Pass separates the south end of Decatur Island from the eastern arm of Lopez Island. It has a minimum width of 350 yards, and the minimum depth of its bed is about 80 feet.

ROSARIO STRAIT

Rosario Strait is located on the east side of Orcas, Blakeley, Decatur, and Lopez islands, and separates them from Fidalgo Island and the mainland to the eastward. Between Lopez and Fidalgo islands Rosario Strait is about five and one-half miles wide and the average depth of its channel is about 240 feet. Between Decatur and Fidalgo islands it is only four and one-half miles wide, but farther to the northward it widens out to surround Cypress, Guemes, Sinclair, and Lummi islands. The smaller channels separating these islands are known by their separate names but they are really a part of Rosario Strait.

Due to the presence of the large islands, the broad expanse of water that forms the southern end of Rosario Strait breaks up into Guemes Channel, Bellingham Channel, and Rosario Strait proper. These channels again unite near the south end of Lummi Island, only to be once more divided into Rosario Strait and Hale Passage, and these merge with the waters of the Gulf of Georgia to the northward. At its northern end the bed of Rosario Strait has an average depth of 240 feet.

BELLINGHAM CHANNEL

Bellingham Channel is that portion of Rosario Strait which separates Cypress Island from Guemes Island. It has an average width of about one and one-half miles, and the average depth of its bed is about 240 feet.

GUEMES CHANNEL

Guemes Channel is that portion of Rosario Strait which separates Guemes Island from Fidalgo Island and from the mainland to the east. The depth of its bed varies between 40 and 270 feet. Near the entrance to Padilla Bay, Guemes Channel turns abruptly towards the north and finally merges with the waters at the north end of Bellingham Channel. To the northeast it merges with the waters of Samish Bay.

HALE PASSAGE

Hale Passage is that portion of Rosario Strait which separates Lummi Island from Portage Island and from the mainland to the east. In places its bed is only 12 feet deep at low tide, due to the encroachment of delta materials from the adjoining streams. To the southeastward it merges with the waters of Bellingham Bay.

Burrows Bay, Fidalgo Bay, Padilla Bay, Samish Bay, and Bellingham Bay occur along the shore of the mainland at the eastern margin of the waters of Rosario Strait.

It is worthy of note that the main channels leading through the San Juan islands have depths which greatly exceed those of the broad open waters to the north and to the south of the archipelago. It is probable that the scouring action of the powerful tidal currents is largely responsible for this condition.